[LLVM][IR] Add support for vector ConstantInt/FP to ConstandFolding:FoldBitCast. (#117163)

Author: paulwalker-arm

llvm/lib/Analysis/ConstantFolding.cpp

@@ -151,8 +151,14 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
     return FoldBitCast(ConstantVector::get(Ops), DestTy, DL);
   }
 
+  // Some of what follows may extend to cover scalable vectors but the current
+  // implementation is fixed length specific.
+  if (!isa<FixedVectorType>(C->getType()))
+    return ConstantExpr::getBitCast(C, DestTy);
+
   // If this is a bitcast from constant vector -> vector, fold it.
-  if (!isa<ConstantDataVector>(C) && !isa<ConstantVector>(C))
+  if (!isa<ConstantDataVector>(C) && !isa<ConstantVector>(C) &&
+      !isa<ConstantInt>(C) && !isa<ConstantFP>(C))
     return ConstantExpr::getBitCast(C, DestTy);
 
   // If the element types match, IR can fold it.
@@ -194,10 +200,9 @@ Constant *FoldBitCast(Constant *C, Type *DestTy, const DataLayout &DL) {
         IntegerType::get(C->getContext(), FPWidth), NumSrcElt);
     // Ask IR to do the conversion now that #elts line up.
     C = ConstantExpr::getBitCast(C, SrcIVTy);
-    // If IR wasn't able to fold it, bail out.
-    if (!isa<ConstantVector>(C) &&  // FIXME: Remove ConstantVector.
-        !isa<ConstantDataVector>(C))
-      return C;
+    assert((isa<ConstantVector>(C) || // FIXME: Remove ConstantVector.
+            isa<ConstantDataVector>(C) || isa<ConstantInt>(C)) &&
+           "Constant folding cannot fail for plain fp->int bitcast!");
   }
 
   // Now we know that the input and output vectors are both integer vectors

llvm/test/Transforms/InstCombine/cast.ll

@@ -2,6 +2,8 @@
 ; Tests to make sure elimination of casts is working correctly
 ; RUN: opt < %s -passes=instcombine -S -data-layout="E-p:64:64:64-p1:32:32:32-p2:64:64:64-p3:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128-n8:16:32:64" | FileCheck %s --check-prefixes=ALL,BE
 ; RUN: opt < %s -passes=instcombine -S -data-layout="e-p:64:64:64-p1:32:32:32-p2:64:64:64-p3:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128-n8:16:32:64" | FileCheck %s --check-prefixes=ALL,LE
+; RUN: opt < %s -passes=instcombine -S -data-layout="E-p:64:64:64-p1:32:32:32-p2:64:64:64-p3:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128-n8:16:32:64" -use-constant-fp-for-fixed-length-splat -use-constant-int-for-fixed-length-splat | FileCheck %s --check-prefixes=ALL,BE
+; RUN: opt < %s -passes=instcombine -S -data-layout="e-p:64:64:64-p1:32:32:32-p2:64:64:64-p3:64:64:64-a0:0:8-f32:32:32-f64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-v64:64:64-v128:128:128-n8:16:32:64" -use-constant-fp-for-fixed-length-splat -use-constant-int-for-fixed-length-splat | FileCheck %s --check-prefixes=ALL,LE
 
 declare void @use_i32(i32)
 declare void @use_v2i32(<2 x i32>)

llvm/test/Transforms/InstSimplify/bitcast-vector-fold.ll

@@ -284,3 +284,11 @@ define <1 x i32> @bitcast_constexpr_scalar_fp_to_vector_int() {
   %res = bitcast float 1.0 to <1 x i32>
   ret <1 x i32> %res
 }
+
+define <2 x i64> @bitcast_constexpr_4f32_2i64_1111() {
+; CHECK-LABEL: @bitcast_constexpr_4f32_2i64_1111(
+; CHECK-NEXT:    ret <2 x i64> splat (i64 4575657222473777152)
+;
+  %res = bitcast <4 x float> splat (float 1.0) to <2 x i64>
+  ret <2 x i64> %res
+}