[LICM] Do not reassociate constant offset GEP (llvm#151492)

LICM tries to reassociate GEPs in order to hoist an invariant GEP.
Currently, it also does this in the case where the GEP has a constant
offset.

This is usually undesirable. From a back-end perspective, constant GEPs
are usually free because they can be folded into addressing modes, so
this just increases register pressume. From a middle-end perspective,
keeping constant offsets last in the chain makes it easier to analyze
the relationship between multiple GEPs on the same base, especially
after CSE.

The worst that can happen here is if we start with something like

```
loop {
   p + 4*x
   p + 4*x + 1
   p + 4*x + 2
   p + 4*x + 3
}
```

And LICM converts it into:

```
p.1 = p + 1
p.2 = p + 2
p.3 = p + 3
loop {
   p + 4*x
   p.1 + 4*x
   p.2 + 4*x
   p.3 + 4*x
}
```

Which is much worse than leaving it for CSE to convert to:
```
loop {
   p2 = p + 4*x
   p2 + 1
   p2 + 2
   p2 + 3
}
```

Author: nikic

llvm/lib/Transforms/Scalar/LICM.cpp

@@ -2508,6 +2508,12 @@ static bool hoistGEP(Instruction &I, Loop &L, ICFLoopSafetyInfo &SafetyInfo,
   if (!GEP)
     return false;
 
+  // Do not try to hoist a constant GEP out of the loop via reassociation.
+  // Constant GEPs can often be folded into addressing modes, and reassociating
+  // them may inhibit CSE of a common base.
+  if (GEP->hasAllConstantIndices())
+    return false;
+
   auto *Src = dyn_cast<GetElementPtrInst>(GEP->getPointerOperand());
   if (!Src || !Src->hasOneUse() || !L.contains(Src))
     return false;

llvm/test/CodeGen/AMDGPU/loop-prefetch-data.ll

@@ -400,9 +400,9 @@ define amdgpu_kernel void @copy_flat_divergent(ptr nocapture %d, ptr nocapture r
 ; GFX12-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_1)
 ; GFX12-NEXT:    v_lshlrev_b32_e32 v0, 4, v0
 ; GFX12-NEXT:    s_wait_kmcnt 0x0
-; GFX12-NEXT:    v_add_co_u32 v2, s1, s6, v0
+; GFX12-NEXT:    v_add_co_u32 v2, s1, v0, s6
 ; GFX12-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_3)
-; GFX12-NEXT:    v_add_co_ci_u32_e64 v3, null, s7, 0, s1
+; GFX12-NEXT:    v_add_co_ci_u32_e64 v3, null, 0, s7, s1
 ; GFX12-NEXT:    v_add_co_u32 v0, s1, s4, v0
 ; GFX12-NEXT:    v_add_co_u32 v2, vcc_lo, 0xb0, v2
 ; GFX12-NEXT:    s_wait_alu 0xf1ff
@@ -438,9 +438,9 @@ define amdgpu_kernel void @copy_flat_divergent(ptr nocapture %d, ptr nocapture r
 ; GFX12-SPREFETCH-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_1)
 ; GFX12-SPREFETCH-NEXT:    v_lshlrev_b32_e32 v0, 4, v0
 ; GFX12-SPREFETCH-NEXT:    s_wait_kmcnt 0x0
-; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, s1, s6, v0
+; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, s1, v0, s6
 ; GFX12-SPREFETCH-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_3)
-; GFX12-SPREFETCH-NEXT:    v_add_co_ci_u32_e64 v3, null, s7, 0, s1
+; GFX12-SPREFETCH-NEXT:    v_add_co_ci_u32_e64 v3, null, 0, s7, s1
 ; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v0, s1, s4, v0
 ; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, vcc_lo, 0xb0, v2
 ; GFX12-SPREFETCH-NEXT:    s_wait_alu 0xf1ff
@@ -531,9 +531,9 @@ define amdgpu_kernel void @copy_global_divergent(ptr addrspace(1) nocapture %d,
 ; GFX12-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_1)
 ; GFX12-NEXT:    v_lshlrev_b32_e32 v0, 4, v0
 ; GFX12-NEXT:    s_wait_kmcnt 0x0
-; GFX12-NEXT:    v_add_co_u32 v2, s1, s6, v0
+; GFX12-NEXT:    v_add_co_u32 v2, s1, v0, s6
 ; GFX12-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_3)
-; GFX12-NEXT:    v_add_co_ci_u32_e64 v3, null, s7, 0, s1
+; GFX12-NEXT:    v_add_co_ci_u32_e64 v3, null, 0, s7, s1
 ; GFX12-NEXT:    v_add_co_u32 v0, s1, s4, v0
 ; GFX12-NEXT:    v_add_co_u32 v2, vcc_lo, 0xb0, v2
 ; GFX12-NEXT:    s_wait_alu 0xf1ff
@@ -569,9 +569,9 @@ define amdgpu_kernel void @copy_global_divergent(ptr addrspace(1) nocapture %d,
 ; GFX12-SPREFETCH-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_1)
 ; GFX12-SPREFETCH-NEXT:    v_lshlrev_b32_e32 v0, 4, v0
 ; GFX12-SPREFETCH-NEXT:    s_wait_kmcnt 0x0
-; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, s1, s6, v0
+; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, s1, v0, s6
 ; GFX12-SPREFETCH-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_3)
-; GFX12-SPREFETCH-NEXT:    v_add_co_ci_u32_e64 v3, null, s7, 0, s1
+; GFX12-SPREFETCH-NEXT:    v_add_co_ci_u32_e64 v3, null, 0, s7, s1
 ; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v0, s1, s4, v0
 ; GFX12-SPREFETCH-NEXT:    v_add_co_u32 v2, vcc_lo, 0xb0, v2
 ; GFX12-SPREFETCH-NEXT:    s_wait_alu 0xf1ff

llvm/test/CodeGen/AMDGPU/memintrinsic-unroll.ll

@@ -6982,7 +6982,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; CHECK-NEXT:    global_store_dwordx4 v[100:101], v[96:99], off offset:16
 ; CHECK-NEXT:    s_cmp_lg_u64 s[4:5], 0x800
 ; CHECK-NEXT:    s_cbranch_scc1 .LBB6_2
-; CHECK-NEXT:  .LBB6_3: ; %Flow9
+; CHECK-NEXT:  .LBB6_3: ; %Flow7
 ; CHECK-NEXT:    s_andn2_saveexec_b32 s8, s6
 ; CHECK-NEXT:    s_cbranch_execz .LBB6_6
 ; CHECK-NEXT:  ; %bb.4: ; %memmove_bwd_loop.preheader
@@ -7048,7 +7048,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; CHECK-NEXT:    global_store_dwordx4 v[100:101], v[96:99], off offset:16
 ; CHECK-NEXT:    s_cmp_eq_u64 s[4:5], s[6:7]
 ; CHECK-NEXT:    s_cbranch_scc0 .LBB6_5
-; CHECK-NEXT:  .LBB6_6: ; %Flow10
+; CHECK-NEXT:  .LBB6_6: ; %Flow8
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
 ;
@@ -7689,7 +7689,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; ALIGNED-NEXT:    global_store_byte v[16:17], v11, off offset:3
 ; ALIGNED-NEXT:    global_store_byte v[16:17], v4, off offset:1
 ; ALIGNED-NEXT:    s_cbranch_scc1 .LBB6_2
-; ALIGNED-NEXT:  .LBB6_3: ; %Flow9
+; ALIGNED-NEXT:  .LBB6_3: ; %Flow7
 ; ALIGNED-NEXT:    s_andn2_saveexec_b32 s8, s6
 ; ALIGNED-NEXT:    s_cbranch_execz .LBB6_6
 ; ALIGNED-NEXT:  ; %bb.4: ; %memmove_bwd_loop.preheader
@@ -8316,7 +8316,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; ALIGNED-NEXT:    global_store_byte v[16:17], v11, off offset:3
 ; ALIGNED-NEXT:    global_store_byte v[16:17], v4, off offset:1
 ; ALIGNED-NEXT:    s_cbranch_scc0 .LBB6_5
-; ALIGNED-NEXT:  .LBB6_6: ; %Flow10
+; ALIGNED-NEXT:  .LBB6_6: ; %Flow8
 ; ALIGNED-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; ALIGNED-NEXT:    s_clause 0x7
 ; ALIGNED-NEXT:    buffer_load_dword v47, off, s[0:3], s32
@@ -8369,7 +8369,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; UNROLL3-NEXT:    global_store_dwordx4 v[0:1], v[2:5], off offset:2032
 ; UNROLL3-NEXT:    ; implicit-def: $vgpr2_vgpr3
 ; UNROLL3-NEXT:    ; implicit-def: $vgpr0_vgpr1
-; UNROLL3-NEXT:  .LBB6_4: ; %Flow7
+; UNROLL3-NEXT:  .LBB6_4: ; %Flow5
 ; UNROLL3-NEXT:    s_andn2_saveexec_b32 s8, s6
 ; UNROLL3-NEXT:    s_cbranch_execz .LBB6_7
 ; UNROLL3-NEXT:  ; %bb.5: ; %memmove_bwd_residual
@@ -8403,7 +8403,7 @@ define void @memmove_p1_p1_sz2048(ptr addrspace(1) align 1 %dst, ptr addrspace(1
 ; UNROLL3-NEXT:    global_store_dwordx4 v[16:17], v[12:15], off offset:32
 ; UNROLL3-NEXT:    s_cmp_eq_u64 s[4:5], s[6:7]
 ; UNROLL3-NEXT:    s_cbranch_scc0 .LBB6_6
-; UNROLL3-NEXT:  .LBB6_7: ; %Flow8
+; UNROLL3-NEXT:  .LBB6_7: ; %Flow6
 ; UNROLL3-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; UNROLL3-NEXT:    s_setpc_b64 s[30:31]
 entry:

llvm/test/CodeGen/AMDGPU/memmove-var-size.ll

@@ -460,10 +460,10 @@ define void @memmove_p0_p4(ptr addrspace(0) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    v_cmpx_ge_u64_e64 v[2:3], v[0:1]
 ; CHECK-NEXT:    s_xor_b32 s7, exec_lo, s6
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_3
-; CHECK-NEXT:  ; %bb.1: ; %Flow34
+; CHECK-NEXT:  ; %bb.1: ; %Flow36
 ; CHECK-NEXT:    s_andn2_saveexec_b32 s6, s7
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_10
-; CHECK-NEXT:  .LBB3_2: ; %Flow35
+; CHECK-NEXT:  .LBB3_2: ; %Flow37
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s6
 ; CHECK-NEXT:    s_waitcnt lgkmcnt(0)
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
@@ -494,7 +494,7 @@ define void @memmove_p0_p4(ptr addrspace(0) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v11, null, 0, v11, s6
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s9
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_5
-; CHECK-NEXT:  .LBB3_6: ; %Flow29
+; CHECK-NEXT:  .LBB3_6: ; %Flow31
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    s_and_saveexec_b32 s8, s4
 ; CHECK-NEXT:    s_cbranch_execz .LBB3_9
@@ -520,7 +520,7 @@ define void @memmove_p0_p4(ptr addrspace(0) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v1, null, 0, v1, s6
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s9
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_8
-; CHECK-NEXT:  .LBB3_9: ; %Flow27
+; CHECK-NEXT:  .LBB3_9: ; %Flow29
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    ; implicit-def: $vgpr6_vgpr7
 ; CHECK-NEXT:    ; implicit-def: $vgpr2_vgpr3
@@ -556,7 +556,7 @@ define void @memmove_p0_p4(ptr addrspace(0) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v5, null, -1, v5, s5
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_12
-; CHECK-NEXT:  .LBB3_13: ; %Flow33
+; CHECK-NEXT:  .LBB3_13: ; %Flow35
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s7
 ; CHECK-NEXT:    s_and_saveexec_b32 s5, vcc_lo
 ; CHECK-NEXT:    s_cbranch_execz .LBB3_16
@@ -584,7 +584,7 @@ define void @memmove_p0_p4(ptr addrspace(0) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    flat_store_dwordx4 v[12:13], v[8:11]
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s7
 ; CHECK-NEXT:    s_cbranch_execnz .LBB3_15
-; CHECK-NEXT:  .LBB3_16: ; %Flow31
+; CHECK-NEXT:  .LBB3_16: ; %Flow33
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s5
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s6
 ; CHECK-NEXT:    s_waitcnt lgkmcnt(0)
@@ -907,10 +907,10 @@ define void @memmove_p1_p1(ptr addrspace(1) align 1 %dst, ptr addrspace(1) align
 ; CHECK-NEXT:    v_cmpx_ge_u64_e64 v[2:3], v[0:1]
 ; CHECK-NEXT:    s_xor_b32 s7, exec_lo, s6
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_3
-; CHECK-NEXT:  ; %bb.1: ; %Flow41
+; CHECK-NEXT:  ; %bb.1: ; %Flow39
 ; CHECK-NEXT:    s_andn2_saveexec_b32 s6, s7
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_10
-; CHECK-NEXT:  .LBB6_2: ; %Flow42
+; CHECK-NEXT:  .LBB6_2: ; %Flow40
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s6
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
 ; CHECK-NEXT:  .LBB6_3: ; %memmove_copy_forward
@@ -940,7 +940,7 @@ define void @memmove_p1_p1(ptr addrspace(1) align 1 %dst, ptr addrspace(1) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v11, null, 0, v11, s6
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s9
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_5
-; CHECK-NEXT:  .LBB6_6: ; %Flow36
+; CHECK-NEXT:  .LBB6_6: ; %Flow34
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    s_and_saveexec_b32 s8, s4
 ; CHECK-NEXT:    s_cbranch_execz .LBB6_9
@@ -966,11 +966,11 @@ define void @memmove_p1_p1(ptr addrspace(1) align 1 %dst, ptr addrspace(1) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v1, null, 0, v1, s6
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s9
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_8
-; CHECK-NEXT:  .LBB6_9: ; %Flow34
+; CHECK-NEXT:  .LBB6_9: ; %Flow32
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    ; implicit-def: $vgpr6_vgpr7
-; CHECK-NEXT:    ; implicit-def: $vgpr2_vgpr3
 ; CHECK-NEXT:    ; implicit-def: $vgpr0_vgpr1
+; CHECK-NEXT:    ; implicit-def: $vgpr2_vgpr3
 ; CHECK-NEXT:    ; implicit-def: $vgpr8_vgpr9
 ; CHECK-NEXT:    ; implicit-def: $vgpr4_vgpr5
 ; CHECK-NEXT:    s_andn2_saveexec_b32 s6, s7
@@ -1002,15 +1002,15 @@ define void @memmove_p1_p1(ptr addrspace(1) align 1 %dst, ptr addrspace(1) align
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v5, null, -1, v5, s5
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_12
-; CHECK-NEXT:  .LBB6_13: ; %Flow40
+; CHECK-NEXT:  .LBB6_13: ; %Flow38
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s7
 ; CHECK-NEXT:    s_and_saveexec_b32 s5, vcc_lo
 ; CHECK-NEXT:    s_cbranch_execz .LBB6_16
 ; CHECK-NEXT:  ; %bb.14: ; %memmove_bwd_main_loop.preheader
-; CHECK-NEXT:    v_add_co_u32 v2, vcc_lo, v2, -16
-; CHECK-NEXT:    v_add_co_ci_u32_e64 v3, null, -1, v3, vcc_lo
 ; CHECK-NEXT:    v_add_co_u32 v0, vcc_lo, v0, -16
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v1, null, -1, v1, vcc_lo
+; CHECK-NEXT:    v_add_co_u32 v2, vcc_lo, v2, -16
+; CHECK-NEXT:    v_add_co_ci_u32_e64 v3, null, -1, v3, vcc_lo
 ; CHECK-NEXT:    s_mov_b32 s7, 0
 ; CHECK-NEXT:    .p2align 6
 ; CHECK-NEXT:  .LBB6_15: ; %memmove_bwd_main_loop
@@ -1030,7 +1030,7 @@ define void @memmove_p1_p1(ptr addrspace(1) align 1 %dst, ptr addrspace(1) align
 ; CHECK-NEXT:    global_store_dwordx4 v[12:13], v[8:11], off
 ; CHECK-NEXT:    s_andn2_b32 exec_lo, exec_lo, s7
 ; CHECK-NEXT:    s_cbranch_execnz .LBB6_15
-; CHECK-NEXT:  .LBB6_16: ; %Flow38
+; CHECK-NEXT:  .LBB6_16: ; %Flow36
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s5
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s6
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
@@ -1181,8 +1181,8 @@ define void @memmove_p1_p4(ptr addrspace(1) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:  .LBB8_9: ; %Flow31
 ; CHECK-NEXT:    s_or_b32 exec_lo, exec_lo, s8
 ; CHECK-NEXT:    ; implicit-def: $vgpr6_vgpr7
-; CHECK-NEXT:    ; implicit-def: $vgpr2_vgpr3
 ; CHECK-NEXT:    ; implicit-def: $vgpr0_vgpr1
+; CHECK-NEXT:    ; implicit-def: $vgpr2_vgpr3
 ; CHECK-NEXT:    ; implicit-def: $vgpr8_vgpr9
 ; CHECK-NEXT:    ; implicit-def: $vgpr4_vgpr5
 ; CHECK-NEXT:    s_andn2_saveexec_b32 s6, s7
@@ -1219,10 +1219,10 @@ define void @memmove_p1_p4(ptr addrspace(1) align 1 %dst, ptr addrspace(4) align
 ; CHECK-NEXT:    s_and_saveexec_b32 s5, vcc_lo
 ; CHECK-NEXT:    s_cbranch_execz .LBB8_16
 ; CHECK-NEXT:  ; %bb.14: ; %memmove_bwd_main_loop.preheader
-; CHECK-NEXT:    v_add_co_u32 v2, vcc_lo, v2, -16
-; CHECK-NEXT:    v_add_co_ci_u32_e64 v3, null, -1, v3, vcc_lo
 ; CHECK-NEXT:    v_add_co_u32 v0, vcc_lo, v0, -16
 ; CHECK-NEXT:    v_add_co_ci_u32_e64 v1, null, -1, v1, vcc_lo
+; CHECK-NEXT:    v_add_co_u32 v2, vcc_lo, v2, -16
+; CHECK-NEXT:    v_add_co_ci_u32_e64 v3, null, -1, v3, vcc_lo
 ; CHECK-NEXT:    s_mov_b32 s7, 0
 ; CHECK-NEXT:    .p2align 6
 ; CHECK-NEXT:  .LBB8_15: ; %memmove_bwd_main_loop