[InstCombine] Set flags when canonicalizing GEP indices (#151516)

nikic · web-flow · commit a71909156e5e · 2025-07-31T15:58:04.000+02:00
When truncating set nsw/nuw based on nusw/nuw. When extending, use zext nneg if nusw+nuw. Proof: https://alive2.llvm.org/ce/z/JA2Yzr
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3184,7 +3184,16 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
       // If we are using a wider index than needed for this platform, shrink
       // it to what we need.  If narrower, sign-extend it to what we need.
       // This explicit cast can make subsequent optimizations more obvious.
-      *I = Builder.CreateIntCast(*I, NewIndexType, true);
+      if (IndexTy->getScalarSizeInBits() <
+          NewIndexType->getScalarSizeInBits()) {
+        if (GEP.hasNoUnsignedWrap() && GEP.hasNoUnsignedSignedWrap())
+          *I = Builder.CreateZExt(*I, NewIndexType, "", /*IsNonNeg=*/true);
+        else
+          *I = Builder.CreateSExt(*I, NewIndexType);
+      } else {
+        *I = Builder.CreateTrunc(*I, NewIndexType, "", GEP.hasNoUnsignedWrap(),
+                                 GEP.hasNoUnsignedSignedWrap());
+      }
       MadeChange = true;
     }
   }
diff --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -356,7 +356,7 @@ define i1 @test13_i16(i16 %X, ptr %P) {
 
 define i1 @test13_i128(i128 %X, ptr %P) {
 ; CHECK-LABEL: @test13_i128(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i128 [[X:%.*]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i128 [[X:%.*]] to i64
 ; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 [[TMP1]], -1
 ; CHECK-NEXT:    ret i1 [[C]]
 ;
@@ -412,7 +412,7 @@ define ptr @test_index_canon_inbounds(ptr %X, i32 %Idx) {
 
 define ptr @test_index_canon_nusw_nuw(ptr %X, i32 %Idx) {
 ; CHECK-LABEL: @test_index_canon_nusw_nuw(
-; CHECK-NEXT:    [[TMP1:%.*]] = sext i32 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = zext nneg i32 [[IDX:%.*]] to i64
 ; CHECK-NEXT:    [[R:%.*]] = getelementptr nusw nuw i32, ptr [[X:%.*]], i64 [[TMP1]]
 ; CHECK-NEXT:    ret ptr [[R]]
 ;
@@ -568,7 +568,7 @@ define i32 @test20(ptr %P, i32 %A, i32 %B) {
 
 define i32 @test20_as1(ptr addrspace(1) %P, i32 %A, i32 %B) {
 ; CHECK-LABEL: @test20_as1(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[A:%.*]] to i16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i32 [[A:%.*]] to i16
 ; CHECK-NEXT:    [[T6:%.*]] = icmp eq i16 [[TMP1]], 0
 ; CHECK-NEXT:    [[T7:%.*]] = zext i1 [[T6]] to i32
 ; CHECK-NEXT:    ret i32 [[T7]]
@@ -1978,4 +1978,94 @@ define ptr @gep_merge_nusw_const(ptr %p, i64 %idx, i64 %idx2) {
   ret ptr %gep
 }
 
+define ptr @gep_index_trunc_nothing(ptr %p, i128 %idx) {
+; CHECK-LABEL: @gep_index_trunc_nothing(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i128 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr i8, ptr %p, i128 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_trunc_nuw(ptr %p, i128 %idx) {
+; CHECK-LABEL: @gep_index_trunc_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nuw i128 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nuw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nuw i8, ptr %p, i128 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_trunc_nusw(ptr %p, i128 %idx) {
+; CHECK-LABEL: @gep_index_trunc_nusw(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i128 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nusw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nusw i8, ptr %p, i128 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_trunc_inbounds(ptr %p, i128 %idx) {
+; CHECK-LABEL: @gep_index_trunc_inbounds(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i128 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr inbounds i8, ptr %p, i128 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_trunc_nusw_nuw(ptr %p, i128 %idx) {
+; CHECK-LABEL: @gep_index_trunc_nusw_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nuw nsw i128 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nusw nuw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nusw nuw i8, ptr %p, i128 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_ext_nothing(ptr %p, i32 %idx) {
+; CHECK-LABEL: @gep_index_ext_nothing(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i32 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr i8, ptr %p, i32 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_ext_nuw(ptr %p, i32 %idx) {
+; CHECK-LABEL: @gep_index_ext_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i32 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nuw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nuw i8, ptr %p, i32 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_ext_nusw(ptr %p, i32 %idx) {
+; CHECK-LABEL: @gep_index_ext_nusw(
+; CHECK-NEXT:    [[TMP1:%.*]] = sext i32 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nuw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nuw i8, ptr %p, i32 %idx
+  ret ptr %gep
+}
+
+define ptr @gep_index_ext_nusw_nuw(ptr %p, i32 %idx) {
+; CHECK-LABEL: @gep_index_ext_nusw_nuw(
+; CHECK-NEXT:    [[TMP1:%.*]] = zext nneg i32 [[IDX:%.*]] to i64
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr nusw nuw i8, ptr [[P:%.*]], i64 [[TMP1]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr nusw nuw i8, ptr %p, i32 %idx
+  ret ptr %gep
+}
+
 !0 = !{!"branch_weights", i32 2, i32 10}
diff --git a/llvm/test/Transforms/InstCombine/icmp-custom-dl.ll b/llvm/test/Transforms/InstCombine/icmp-custom-dl.ll
@@ -39,9 +39,9 @@ define i1 @test59_as1(ptr addrspace(1) %foo) {
 
 define i1 @test60(ptr %foo, i64 %i, i64 %j) {
 ; CHECK-LABEL: @test60(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[I:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[I:%.*]] to i32
 ; CHECK-NEXT:    [[GEP1_IDX:%.*]] = shl nsw i32 [[TMP1]], 2
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[J:%.*]] to i32
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc nsw i64 [[J:%.*]] to i32
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[GEP1_IDX]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
@@ -53,9 +53,9 @@ define i1 @test60(ptr %foo, i64 %i, i64 %j) {
 
 define i1 @test60_as1(ptr addrspace(1) %foo, i64 %i, i64 %j) {
 ; CHECK-LABEL: @test60_as1(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[I:%.*]] to i16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[I:%.*]] to i16
 ; CHECK-NEXT:    [[GEP1_IDX:%.*]] = shl nsw i16 [[TMP1]], 2
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[J:%.*]] to i16
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc nsw i64 [[J:%.*]] to i16
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[GEP1_IDX]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
@@ -69,7 +69,7 @@ define i1 @test60_as1(ptr addrspace(1) %foo, i64 %i, i64 %j) {
 ; bitcast. This uses the same sized addrspace.
 define i1 @test60_addrspacecast(ptr %foo, i64 %i, i64 %j) {
 ; CHECK-LABEL: @test60_addrspacecast(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[J:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[J:%.*]] to i32
 ; CHECK-NEXT:    [[I_TR:%.*]] = trunc i64 [[I:%.*]] to i32
 ; CHECK-NEXT:    [[TMP2:%.*]] = shl i32 [[I_TR]], 2
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[TMP2]], [[TMP1]]
diff --git a/llvm/test/Transforms/InstCombine/icmp-gep.ll b/llvm/test/Transforms/InstCombine/icmp-gep.ll
@@ -286,8 +286,7 @@ define i1 @PR8882(i64 %i) {
 
 define i1 @test24_as1(i64 %i) {
 ; CHECK-LABEL: @test24_as1(
-; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[I:%.*]], 65535
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[TMP1]], 1000
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i64 [[TMP1:%.*]], 1000
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %p1 = getelementptr inbounds i32, ptr addrspace(1) @X_as1, i64 %i
@@ -449,9 +448,9 @@ define i1 @test_gep_eq_no_inbounds(ptr %foo, i64 %i, i64 %j) {
 
 define i1 @test60_as1(ptr addrspace(1) %foo, i64 %i, i64 %j) {
 ; CHECK-LABEL: @test60_as1(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[I:%.*]] to i16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[I:%.*]] to i16
 ; CHECK-NEXT:    [[GEP1_IDX:%.*]] = shl nsw i16 [[TMP1]], 2
-; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[J:%.*]] to i16
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc nsw i64 [[J:%.*]] to i16
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i16 [[GEP1_IDX]], [[TMP2]]
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
diff --git a/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll b/llvm/test/Transforms/InstCombine/indexed-gep-compares.ll
@@ -376,7 +376,7 @@ define i1 @test8(ptr %in, i64 %offset) {
 ; CHECK-NEXT:    [[LD:%.*]] = load i64, ptr [[IN:%.*]], align 8
 ; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[LD]] to i32
 ; CHECK-NEXT:    [[CASTI8:%.*]] = inttoptr i32 [[TMP0]] to ptr
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[OFFSET:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[OFFSET:%.*]] to i32
 ; CHECK-NEXT:    [[GEPI8:%.*]] = getelementptr inbounds i8, ptr [[CASTI8]], i32 [[TMP1]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[LD]] to i32
 ; CHECK-NEXT:    [[PTRCAST:%.*]] = inttoptr i32 [[TMP2]] to ptr
diff --git a/llvm/test/Transforms/InstCombine/load-cmp.ll b/llvm/test/Transforms/InstCombine/load-cmp.ll
@@ -293,8 +293,7 @@ define i1 @test10_struct_arr_i16(i16 %x) {
 
 define i1 @test10_struct_arr_i64(i64 %x) {
 ; CHECK-LABEL: @test10_struct_arr_i64(
-; CHECK-NEXT:    [[TMP1:%.*]] = and i64 [[X:%.*]], 4294967295
-; CHECK-NEXT:    [[R:%.*]] = icmp ne i64 [[TMP1]], 1
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i64 [[TMP1:%.*]], 1
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
   %p = getelementptr inbounds [4 x %Foo], ptr @GStructArr, i64 0, i64 %x, i32 2
@@ -331,7 +330,7 @@ define i1 @test10_struct_arr_noinbounds_i64(i64 %x) {
 
 define i1 @pr93017(i64 %idx) {
 ; CHECK-LABEL: @pr93017(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[IDX:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[IDX:%.*]] to i32
 ; CHECK-NEXT:    [[GEP:%.*]] = getelementptr inbounds [2 x ptr], ptr @table, i32 0, i32 [[TMP1]]
 ; CHECK-NEXT:    [[V:%.*]] = load ptr, ptr [[GEP]], align 4
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ne ptr [[V]], null
diff --git a/llvm/test/Transforms/InstCombine/pr39908.ll b/llvm/test/Transforms/InstCombine/pr39908.ll
@@ -19,7 +19,7 @@ define i1 @test(ptr %p, i32 %n) {
 ; Same test using 64-bit indices.
 define i1 @test64(ptr %p, i64 %n) {
 ; CHECK-LABEL: @test64(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[N:%.*]] to i32
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
@@ -32,7 +32,7 @@ define i1 @test64(ptr %p, i64 %n) {
 ; Here the offset overflows and is treated modulo 2^32. This is UB.
 define i1 @test64_overflow(ptr %p, i64 %n) {
 ; CHECK-LABEL: @test64_overflow(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[N:%.*]] to i32
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
diff --git a/llvm/test/Transforms/InstCombine/sub-gep.ll b/llvm/test/Transforms/InstCombine/sub-gep.ll
@@ -394,7 +394,7 @@ define i64 @negative_ptrtoint_sub_zext_ptrtoint(ptr %p, i32 %offset) {
 
 define i16 @test25_as1(ptr addrspace(1) %P, i64 %A) {
 ; CHECK-LABEL: @test25_as1(
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc i64 [[A:%.*]] to i16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[A:%.*]] to i16
 ; CHECK-NEXT:    [[B_IDX:%.*]] = shl nsw i16 [[TMP1]], 1
 ; CHECK-NEXT:    [[GEPDIFF:%.*]] = add nsw i16 [[B_IDX]], -84
 ; CHECK-NEXT:    ret i16 [[GEPDIFF]]
