[InstCombine] Allow fptrunc (fpext X)) to be reduced to a single fpex…

…t/ftrunc

If we are only truncating bits from the extend we should be able to just use a smaller extend.

If we are truncating more than the extend we should be able to just use a fptrunc since the presense of the fpextend shouldn't affect rounding.

Differential Revision: https://reviews.llvm.org/D43970

llvm-svn: 326595

llvm/lib/IR/Instructions.cpp

@@ -2173,7 +2173,7 @@ unsigned CastInst::isEliminableCastPair(
     { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // UIToFP         +- firstOp
     { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // SIToFP         |
     { 99,99,99, 0, 0,99,99, 0, 0,99,99, 4, 0}, // FPTrunc        |
-    { 99,99,99, 2, 2,99,99,10, 2,99,99, 4, 0}, // FPExt          |
+    { 99,99,99, 2, 2,99,99, 8, 2,99,99, 4, 0}, // FPExt          |
     {  1, 0, 0,99,99, 0, 0,99,99,99, 7, 3, 0}, // PtrToInt       |
     { 99,99,99,99,99,99,99,99,99,11,99,15, 0}, // IntToPtr       |
     {  5, 5, 5, 6, 6, 5, 5, 6, 6,16, 5, 1,14}, // BitCast        |
@@ -2267,12 +2267,6 @@ unsigned CastInst::isEliminableCastPair(
     case 9:
       // zext, sext -> zext, because sext can't sign extend after zext
       return Instruction::ZExt;
-    case 10:
-      // fpext followed by ftrunc is allowed if the bit size returned to is
-      // the same as the original, in which case its just a bitcast
-      if (SrcTy == DstTy)
-        return Instruction::BitCast;
-      return 0; // If the types are not the same we can't eliminate it.
     case 11: {
       // inttoptr, ptrtoint -> bitcast if SrcSize<=PtrSize and SrcSize==DstSize
       if (!MidIntPtrTy)

llvm/test/Transforms/InstCombine/double-float-shrink-2.ll

@@ -448,8 +448,7 @@ define half @test_mismatched_type_intrin_fabs_fast_double_src(double %D) {
 define float @test_shrink_intrin_floor_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_floor_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.floor.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -461,8 +460,7 @@ define float @test_shrink_intrin_floor_fp16_src(half %C) {
 define float @test_shrink_intrin_ceil_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_ceil_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.ceil.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -474,8 +472,7 @@ define float @test_shrink_intrin_ceil_fp16_src(half %C) {
 define float @test_shrink_intrin_round_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_round_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.round.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -487,8 +484,7 @@ define float @test_shrink_intrin_round_fp16_src(half %C) {
 define float @test_shrink_intrin_nearbyint_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_nearbyint_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.nearbyint.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -500,8 +496,7 @@ define float @test_shrink_intrin_nearbyint_fp16_src(half %C) {
 define float @test_shrink_intrin_trunc_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_trunc_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.trunc.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -513,8 +508,7 @@ define float @test_shrink_intrin_trunc_fp16_src(half %C) {
 define float @test_shrink_intrin_fabs_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_fabs_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call half @llvm.fabs.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double
@@ -527,8 +521,7 @@ define float @test_shrink_intrin_fabs_fp16_src(half %C) {
 define float @test_shrink_intrin_fabs_fast_fp16_src(half %C) {
 ; ALL-LABEL: @test_shrink_intrin_fabs_fast_fp16_src(
 ; ALL-NEXT:    [[E:%.*]] = call fast half @llvm.fabs.f16(half [[C:%.*]])
-; ALL-NEXT:    [[TMP1:%.*]] = fpext half [[E]] to double
-; ALL-NEXT:    [[F:%.*]] = fptrunc double [[TMP1]] to float
+; ALL-NEXT:    [[F:%.*]] = fpext half [[E]] to float
 ; ALL-NEXT:    ret float [[F]]
 ;
   %D = fpext half %C to double

llvm/test/Transforms/InstCombine/fpextend.ll

@@ -102,8 +102,7 @@ define <2 x float> @not_half_shrinkable(<2 x float> %x) {
 
 define half @test7(float %a) nounwind {
 ; CHECK-LABEL: @test7(
-; CHECK-NEXT:    [[Y:%.*]] = fpext float [[A:%.*]] to double
-; CHECK-NEXT:    [[Z:%.*]] = fptrunc double [[Y]] to half
+; CHECK-NEXT:    [[Z:%.*]] = fptrunc float [[A:%.*]] to half
 ; CHECK-NEXT:    ret half [[Z]]
 ;
   %y = fpext float %a to double
@@ -113,8 +112,7 @@ define half @test7(float %a) nounwind {
 
 define float @test8(half %a) nounwind {
 ; CHECK-LABEL: @test8(
-; CHECK-NEXT:    [[Y:%.*]] = fpext half [[A:%.*]] to double
-; CHECK-NEXT:    [[Z:%.*]] = fptrunc double [[Y]] to float
+; CHECK-NEXT:    [[Z:%.*]] = fpext half [[A:%.*]] to float
 ; CHECK-NEXT:    ret float [[Z]]
 ;
   %y = fpext half %a to double