Fix X86's isTruncateFree to not claim that truncate to i1 is free. This fixes Bill's testcase that failed for r48491.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@48542 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 2 insertions, 46 deletions

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index 1588b49..ceda932 100644
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1647,47 +1647,3 @@ The coalescer could coalesce "edx" with "eax" to avoid the movl in LBB1_2
 if it commuted the addl in LBB1_1.
 
 //===---------------------------------------------------------------------===//
-
-These two functions perform identical operations:
-
-define i32 @test(i32 %f12) {
-	%tmp7.25 = lshr i32 %f12, 16		
-	%tmp7.26 = trunc i32 %tmp7.25 to i8
-	%tmp78.2 = sext i8 %tmp7.26 to i32
-	ret i32 %tmp78.2
-}
-
-define i32 @test2(i32 %f12) {
-	%f11 = shl i32 %f12, 8
-	%tmp7.25 = ashr i32 %f11, 24
-	ret i32 %tmp7.25
-}
-
-but the first compiles into significantly better code on x86-32:
-
-_test:
-	movsbl	6(%esp), %eax
-	ret
-_test2:
-	movl	4(%esp), %eax
-	shll	$8, %eax
-	sarl	$24, %eax
-	ret
-        
-and on x86-64:
-
-_test:
-	shrl	$16, %edi
-	movsbl	%dil, %eax
-	ret
-_test2:
-	shll	$8, %edi
-	movl	%edi, %eax
-	sarl	$24, %eax
-	ret
-
-I would like instcombine to canonicalize the first into the second (since it is
-shorter and doesn't involve type width changes) but the x86 backend needs to do
-the right thing with the later sequence first.
-
-//===---------------------------------------------------------------------===//
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 5a05aba..93fb802 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -5662,7 +5662,7 @@ bool X86TargetLowering::isTruncateFree(const Type *Ty1, const Type *Ty2) const {
     return false;
   unsigned NumBits1 = Ty1->getPrimitiveSizeInBits();
   unsigned NumBits2 = Ty2->getPrimitiveSizeInBits();
-  if (NumBits1 <= NumBits2)
+  if (NumBits1 <= NumBits2 || NumBits2 < 8)
     return false;
   return Subtarget->is64Bit() || NumBits1 < 64;
 }
@@ -5673,7 +5673,7 @@ bool X86TargetLowering::isTruncateFree(MVT::ValueType VT1,
     return false;
   unsigned NumBits1 = MVT::getSizeInBits(VT1);
   unsigned NumBits2 = MVT::getSizeInBits(VT2);
-  if (NumBits1 <= NumBits2)
+  if (NumBits1 <= NumBits2 || NumBits2 < 8)
     return false;
   return Subtarget->is64Bit() || NumBits1 < 64;
 }