[PATCH] D136763: [InstCombine] Don't change switch table from desirable to illegal types

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: spatel, dendibakh, ahatanak.
Herald added subscribers: hiraditya, kristof.beyls.
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In InstCombine we treat i8/i16 as desirable, even if they are not legal. The current logic in shouldChangeType will decide to convert from an illegal but desirable type (such as an i8) to an illegal and undesirable type (such as i3). This patch prevents changing the switch conditions to an odd type on like Arm/AArch64 where i8/i16 are not legal.

This is the same issue as https://reviews.llvm.org/D54115. In the case I was looking it is was converting an i32 switch to an i8 switch, which then became a i3 switch.


https://reviews.llvm.org/D136763

Files:
  llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
  llvm/test/Transforms/InstCombine/known-phi-recurse.ll
  llvm/test/Transforms/InstCombine/narrow-switch.ll
  llvm/test/Transforms/PhaseOrdering/pr44461-br-to-switch-rotate.ll


Index: llvm/test/Transforms/PhaseOrdering/pr44461-br-to-switch-rotate.ll
===================================================================
--- llvm/test/Transforms/PhaseOrdering/pr44461-br-to-switch-rotate.ll
+++ llvm/test/Transforms/PhaseOrdering/pr44461-br-to-switch-rotate.ll
@@ -10,15 +10,15 @@
 ; CHECK-NEXT:    br label [[BB10:%.*]]
 ; CHECK:       bb10:
 ; CHECK-NEXT:    [[ITER1_SROA_5_0:%.*]] = phi i64 [ 100000, [[START:%.*]] ], [ [[SPEC_SELECT:%.*]], [[BB3_I_I:%.*]] ]
-; CHECK-NEXT:    [[ITER1_SROA_9_0:%.*]] = phi i2 [ -2, [[START]] ], [ [[TMP3:%.*]], [[BB3_I_I]] ]
+; CHECK-NEXT:    [[ITER1_SROA_9_0:%.*]] = phi i8 [ 2, [[START]] ], [ [[TMP3:%.*]], [[BB3_I_I]] ]
 ; CHECK-NEXT:    [[COUNT_1:%.*]] = phi i64 [ 0, [[START]] ], [ [[TMP4:%.*]], [[BB3_I_I]] ]
-; CHECK-NEXT:    switch i2 [[ITER1_SROA_9_0]], label [[BB12:%.*]] [
-; CHECK-NEXT:    i2 -2, label [[BB3_I_I]]
-; CHECK-NEXT:    i2 0, label [[BB3_I_I]]
+; CHECK-NEXT:    switch i8 [[ITER1_SROA_9_0]], label [[BB12:%.*]] [
+; CHECK-NEXT:    i8 2, label [[BB3_I_I]]
+; CHECK-NEXT:    i8 0, label [[BB3_I_I]]
 ; CHECK-NEXT:    ]
 ; CHECK:       bb3.i.i:
 ; CHECK-NEXT:    [[TMP2:%.*]] = icmp eq i64 [[ITER1_SROA_5_0]], 0
-; CHECK-NEXT:    [[TMP3]] = zext i1 [[TMP2]] to i2
+; CHECK-NEXT:    [[TMP3]] = zext i1 [[TMP2]] to i8
 ; CHECK-NEXT:    [[_5_0_I_I_I_I:%.*]] = add i64 [[ITER1_SROA_5_0]], -1
 ; CHECK-NEXT:    [[SPEC_SELECT]] = select i1 [[TMP2]], i64 0, i64 [[_5_0_I_I_I_I]]
 ; CHECK-NEXT:    [[TMP4]] = add i64 [[COUNT_1]], [[ITER1_SROA_5_0]]
Index: llvm/test/Transforms/InstCombine/narrow-switch.ll
===================================================================
--- llvm/test/Transforms/InstCombine/narrow-switch.ll
+++ llvm/test/Transforms/InstCombine/narrow-switch.ll
@@ -138,11 +138,10 @@
 define i8 @PR31260(i8 %x) {
 ; ALL-LABEL: @PR31260(
 ; ALL-NEXT:  entry:
-; ALL-NEXT:    [[TMP0:%.*]] = trunc i8 %x to i2
-; ALL-NEXT:    [[TRUNC:%.*]] = and i2 [[TMP0]], -2
-; ALL-NEXT:    switch i2 [[TRUNC]], label %exit [
-; ALL-NEXT:    i2 0, label %case126
-; ALL-NEXT:    i2 -2, label %case124
+; ALL-NEXT:    [[T4:%.*]] = and i8 [[X:%.*]], 2
+; ALL-NEXT:    switch i8 [[T4]], label [[EXIT:%.*]] [
+; ALL-NEXT:    i8 0, label [[CASE126:%.*]]
+; ALL-NEXT:    i8 2, label [[CASE124:%.*]]
 ; ALL-NEXT:    ]
 ; ALL:       exit:
 ; ALL-NEXT:    ret i8 1
Index: llvm/test/Transforms/InstCombine/known-phi-recurse.ll
===================================================================
--- llvm/test/Transforms/InstCombine/known-phi-recurse.ll
+++ llvm/test/Transforms/InstCombine/known-phi-recurse.ll
@@ -92,12 +92,11 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[Y:%.*]] = call i64 @llvm.ctpop.i64(i64 [[X:%.*]]), !range [[RNG0]]
 ; CHECK-NEXT:    [[TRUNC:%.*]] = trunc i64 [[Y]] to i32
-; CHECK-NEXT:    [[TRUNC1:%.*]] = trunc i64 [[Y]] to i7
-; CHECK-NEXT:    switch i7 [[TRUNC1]], label [[END:%.*]] [
-; CHECK-NEXT:    i7 1, label [[ONE:%.*]]
-; CHECK-NEXT:    i7 2, label [[TWO:%.*]]
-; CHECK-NEXT:    i7 3, label [[THREE:%.*]]
-; CHECK-NEXT:    i7 4, label [[FOUR:%.*]]
+; CHECK-NEXT:    switch i32 [[TRUNC]], label [[END:%.*]] [
+; CHECK-NEXT:    i32 1, label [[ONE:%.*]]
+; CHECK-NEXT:    i32 2, label [[TWO:%.*]]
+; CHECK-NEXT:    i32 3, label [[THREE:%.*]]
+; CHECK-NEXT:    i32 4, label [[FOUR:%.*]]
 ; CHECK-NEXT:    ]
 ; CHECK:       one:
 ; CHECK-NEXT:    [[A:%.*]] = add nuw nsw i32 [[TRUNC]], 1
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -240,7 +240,7 @@
 
   // If this is a legal integer from type, and the result would be an illegal
   // type, don't do the transformation.
-  if (FromLegal && !ToLegal)
+  if ((FromLegal || isDesirableIntType(FromWidth)) && !ToLegal)
     return false;
 
   // Otherwise, if both are illegal, do not increase the size of the result. We


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