Fix known zero bits for addrspacecast.

Currently LLVM assumes that a pointer addrspacecasted to a different addr space is equivalent to trunc or zext bitwise, which is not true. For example, in amdgcn target, when a null pointer is addrspacecasted from addr space 4 to 0, its value is changed from i64 0 to i32 -1.

This patch teaches LLVM not to assume known bits of addrspacecast instruction to its operand.

Differential Revision: https://reviews.llvm.org/D26803


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@287545 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ValueTracking.cpp

@@ -1025,7 +1025,6 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
     break; // Can't work with floating point.
   case Instruction::PtrToInt:
   case Instruction::IntToPtr:
-  case Instruction::AddrSpaceCast: // Pointers could be different sizes.
     // Fall through and handle them the same as zext/trunc.
     LLVM_FALLTHROUGH;
   case Instruction::ZExt:

test/Analysis/ValueTracking/knownzero-addrspacecast.ll

@@ -0,0 +1,24 @@
+; RUN: opt -instcombine -S < %s | FileCheck %s
+
+; When a pointer is addrspacecasted to a another addr space, we cannot assume
+; anything about the new bits.
+
+target datalayout = "p:32:32-p3:32:32-p4:64:64"
+
+; CHECK-LABEL: @test_shift
+; CHECK-NOT: ret i64 0
+define i64 @test_shift(i8* %p) {
+  %g = addrspacecast i8* %p to i8 addrspace(4)*
+  %i = ptrtoint i8 addrspace(4)* %g to i64
+  %shift = lshr i64 %i, 32
+  ret i64 %shift
+}
+
+; CHECK-LABEL: @test_null
+; A null pointer casted to another addr space may no longer have null value.
+; CHECK-NOT: ret i32 0
+define i32 @test_null() {
+  %g = addrspacecast i8* null to i8 addrspace(3)*
+  %i = ptrtoint i8 addrspace(3)* %g to i32
+  ret i32 %i
+}

test/Transforms/InstCombine/loadstore-alignment.ll

@@ -14,33 +14,6 @@ define <2 x i64> @static_hem() {
   ret <2 x i64> %tmp1
 }
 
-; CHECK-LABEL: @static_hem_addrspacecast(
-; CHECK: , align 16
-define <2 x i64> @static_hem_addrspacecast() {
-  %t = getelementptr <2 x i64>, <2 x i64>* @x, i32 7
-  %t.asc = addrspacecast <2 x i64>* %t to <2 x i64> addrspace(1)*
-  %tmp1 = load <2 x i64>, <2 x i64> addrspace(1)* %t.asc, align 1
-  ret <2 x i64> %tmp1
-}
-
-; CHECK-LABEL: @static_hem_addrspacecast_smaller_ptr(
-; CHECK: , align 16
-define <2 x i64> @static_hem_addrspacecast_smaller_ptr() {
-  %t = getelementptr <2 x i64>, <2 x i64>* @x, i32 7
-  %t.asc = addrspacecast <2 x i64>* %t to <2 x i64> addrspace(2)*
-  %tmp1 = load <2 x i64>, <2 x i64> addrspace(2)* %t.asc, align 1
-  ret <2 x i64> %tmp1
-}
-
-; CHECK-LABEL: @static_hem_addrspacecast_larger_ptr(
-; CHECK: , align 16
-define <2 x i64> @static_hem_addrspacecast_larger_ptr() {
-  %t = getelementptr <2 x i64>, <2 x i64> addrspace(2)* @x.as2, i32 7
-  %t.asc = addrspacecast <2 x i64> addrspace(2)* %t to <2 x i64> addrspace(1)*
-  %tmp1 = load <2 x i64>, <2 x i64> addrspace(1)* %t.asc, align 1
-  ret <2 x i64> %tmp1
-}
-
 ; CHECK-LABEL: @hem(
 ; CHECK: , align 16
 define <2 x i64> @hem(i32 %i) {