[PATCH] D57041: [ARM][CGP] Check trunc value size before replacing

[Sam Parker via Phabricator via llvm-commits]

samparker created this revision.
samparker added a reviewer: SjoerdMeijer.
Herald added subscribers: kristof.beyls, javed.absar.

In the last stage of type promotion, we replace any zext that uses a new trunc with the operand of the trunc. This is okay when we only allowed one type to be optimised, but now its the case that the trunc maybe needed to produce a more narrow type than the one we were optimising for. So we need to check this before doing the replacement.


https://reviews.llvm.org/D57041

Files:
  lib/Target/ARM/ARMCodeGenPrepare.cpp
  test/CodeGen/ARM/CGP/arm-cgp-casts.ll


Index: test/CodeGen/ARM/CGP/arm-cgp-casts.ll
===================================================================
--- test/CodeGen/ARM/CGP/arm-cgp-casts.ll
+++ test/CodeGen/ARM/CGP/arm-cgp-casts.ll
@@ -588,3 +588,47 @@
   store i8 %cond, i8* @a, align 1
   ret void
 }
+
+; CHECK-LABEL: dont_replace_trunc_1
+; CHECK: cmp
+; CHECK: uxtb
+define void @dont_replace_trunc_1(i8* %a, i16* %b, i16* %c, i32* %d, i8* %e, i32* %f) {
+entry:
+  %0 = load i16, i16* %c, align 2
+  %1 = load i16, i16* %b, align 2
+  %conv = sext i16 %1 to i32
+  store i32 %conv, i32* %f, align 4
+  %2 = trunc i16 %1 to i8
+  %conv1 = and i8 %2, 1
+  store i8 %conv1, i8* %e, align 1
+  %3 = load i8, i8* %a, align 1
+  %narrow = mul nuw i8 %3, %conv1
+  %mul = zext i8 %narrow to i32
+  store i32 %mul, i32* %d, align 4
+  %4 = zext i8 %narrow to i16
+  %conv5 = or i16 %0, %4
+  %tobool = icmp eq i16 %conv5, 0
+  br i1 %tobool, label %if.end, label %for.cond
+
+for.cond:                                         ; preds = %entry, %for.cond
+  br label %for.cond
+
+if.end:                                           ; preds = %entry
+  ret void
+}
+
+; CHECK-LABEL: dont_replace_trunc_2
+; CHECK: cmp
+; CHECK: uxtb
+define i32 @dont_replace_trunc_2(i16* %a, i8* %b) {
+entry:
+  %0 = load i16, i16* %a, align 2
+  %cmp = icmp ugt i16 %0, 8
+  %narrow = select i1 %cmp, i16 %0, i16 0
+  %cond = trunc i16 %narrow to i8
+  %1 = load i8, i8* %b, align 1
+  %or = or i8 %1, %cond
+  store i8 %or, i8* %b, align 1
+  %conv5 = zext i8 %or to i32
+  ret i32 %conv5
+}
Index: lib/Target/ARM/ARMCodeGenPrepare.cpp
===================================================================
--- lib/Target/ARM/ARMCodeGenPrepare.cpp
+++ lib/Target/ARM/ARMCodeGenPrepare.cpp
@@ -685,10 +685,10 @@
   // Some zexts will now have become redundant, along with their trunc
   // operands, so remove them
   for (auto V : *Visited) {
-    if (!isa<CastInst>(V))
+    if (!isa<ZExtInst>(V))
       continue;
 
-    auto ZExt = cast<CastInst>(V);
+    auto ZExt = cast<ZExtInst>(V);
     if (ZExt->getDestTy() != ExtTy)
       continue;
 
@@ -700,9 +700,10 @@
       continue;
     }
 
-    // For any truncs that we insert to handle zexts, we can replace the
-    // result of the zext with the input to the trunc.
-    if (NewInsts.count(Src) && isa<ZExtInst>(V) && isa<TruncInst>(Src)) {
+    // Unless they produce a value that is narrower than ExtTy, we can
+    // we can replace the result of the zext with the input of a newly
+    // inserted the trunc.
+    if (NewInsts.count(Src) && isa<TruncInst>(Src) && EqualTypeSize(Src)) {
       auto *Trunc = cast<TruncInst>(Src);
       assert(Trunc->getOperand(0)->getType() == ExtTy &&
              "expected inserted trunc to be operating on i32");


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