diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -34040,6 +34040,11 @@
   Known.resetAll();
   switch (Opc) {
   default: break;
+  case X86ISD::BSR: {
+    // TODO: Bound with input known bits?
+    Known.Zero.setBitsFrom(Log2_32(BitWidth));
+    break;
+  }
   case X86ISD::SETCC:
     Known.Zero.setBitsFrom(1);
     break;
diff --git a/llvm/test/CodeGen/X86/clz.ll b/llvm/test/CodeGen/X86/clz.ll
--- a/llvm/test/CodeGen/X86/clz.ll
+++ b/llvm/test/CodeGen/X86/clz.ll
@@ -245,7 +245,7 @@
 ; X86-NOCMOV-NEXT:  # %bb.2:
 ; X86-NOCMOV-NEXT:    bsrl {{[0-9]+}}(%esp), %eax
 ; X86-NOCMOV-NEXT:    xorl $31, %eax
-; X86-NOCMOV-NEXT:    addl $32, %eax
+; X86-NOCMOV-NEXT:    orl $32, %eax
 ; X86-NOCMOV-NEXT:    xorl %edx, %edx
 ; X86-NOCMOV-NEXT:    retl
 ; X86-NOCMOV-NEXT:  .LBB7_1:
@@ -261,7 +261,7 @@
 ; X86-CMOV-NEXT:    xorl $31, %edx
 ; X86-CMOV-NEXT:    bsrl {{[0-9]+}}(%esp), %eax
 ; X86-CMOV-NEXT:    xorl $31, %eax
-; X86-CMOV-NEXT:    addl $32, %eax
+; X86-CMOV-NEXT:    orl $32, %eax
 ; X86-CMOV-NEXT:    testl %ecx, %ecx
 ; X86-CMOV-NEXT:    cmovnel %edx, %eax
 ; X86-CMOV-NEXT:    xorl %edx, %edx
diff --git a/llvm/test/CodeGen/X86/pr40090.ll b/llvm/test/CodeGen/X86/pr40090.ll
--- a/llvm/test/CodeGen/X86/pr40090.ll
+++ b/llvm/test/CodeGen/X86/pr40090.ll
@@ -5,7 +5,7 @@
 ; CHECK-LABEL: foo:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    bsrq %rdi, %rax
-; CHECK-NEXT:    xorq $64, %rax
+; CHECK-NEXT:    orq $64, %rax
 ; CHECK-NEXT:    bsrq %rsi, %rcx
 ; CHECK-NEXT:    cmoveq %rax, %rcx
 ; CHECK-NEXT:    movl $63, %eax
diff --git a/llvm/test/CodeGen/X86/scheduler-backtracking.ll b/llvm/test/CodeGen/X86/scheduler-backtracking.ll
--- a/llvm/test/CodeGen/X86/scheduler-backtracking.ll
+++ b/llvm/test/CodeGen/X86/scheduler-backtracking.ll
@@ -268,7 +268,7 @@
 ; ILP-NEXT:    andq %rdx, %r10
 ; ILP-NEXT:    bsrq %r10, %rdx
 ; ILP-NEXT:    xorq $63, %r8
-; ILP-NEXT:    addq $64, %rcx
+; ILP-NEXT:    orq $64, %rcx
 ; ILP-NEXT:    testq %rdi, %rdi
 ; ILP-NEXT:    movq $0, 24(%rax)
 ; ILP-NEXT:    movq $0, 16(%rax)
@@ -306,7 +306,7 @@
 ; HYBRID-NEXT:    andq %rcx, %rdi
 ; HYBRID-NEXT:    bsrq %rdi, %rcx
 ; HYBRID-NEXT:    xorq $63, %rcx
-; HYBRID-NEXT:    addq $64, %rcx
+; HYBRID-NEXT:    orq $64, %rcx
 ; HYBRID-NEXT:    testq %r9, %r9
 ; HYBRID-NEXT:    cmovneq %r8, %rcx
 ; HYBRID-NEXT:    andq %rdx, %r10
@@ -346,7 +346,7 @@
 ; BURR-NEXT:    andq %rcx, %rdi
 ; BURR-NEXT:    bsrq %rdi, %rcx
 ; BURR-NEXT:    xorq $63, %rcx
-; BURR-NEXT:    addq $64, %rcx
+; BURR-NEXT:    orq $64, %rcx
 ; BURR-NEXT:    testq %r9, %r9
 ; BURR-NEXT:    cmovneq %r8, %rcx
 ; BURR-NEXT:    andq %rdx, %r10
@@ -388,7 +388,7 @@
 ; SRC-NEXT:    xorq $63, %rcx
 ; SRC-NEXT:    bsrq %r9, %rdx
 ; SRC-NEXT:    xorq $63, %rdx
-; SRC-NEXT:    addq $64, %rdx
+; SRC-NEXT:    orq $64, %rdx
 ; SRC-NEXT:    testq %rdi, %rdi
 ; SRC-NEXT:    cmovneq %rcx, %rdx
 ; SRC-NEXT:    bsrq %r10, %rcx
@@ -434,7 +434,7 @@
 ; LIN-NEXT:    andq %rcx, %rsi
 ; LIN-NEXT:    bsrq %rsi, %rcx
 ; LIN-NEXT:    xorq $63, %rcx
-; LIN-NEXT:    addq $64, %rcx
+; LIN-NEXT:    orq $64, %rcx
 ; LIN-NEXT:    sbbq %r8, %r9
 ; LIN-NEXT:    andq %r8, %r9
 ; LIN-NEXT:    bsrq %r9, %rdi
@@ -476,7 +476,7 @@
 ; ILP-NEXT:    andq %r10, %r8
 ; ILP-NEXT:    bsrq %r8, %r10
 ; ILP-NEXT:    xorq $63, %r10
-; ILP-NEXT:    addq $64, %rdi
+; ILP-NEXT:    orq $64, %rdi
 ; ILP-NEXT:    bsrq %rdx, %r11
 ; ILP-NEXT:    notq %rsi
 ; ILP-NEXT:    testq %r8, %r8
@@ -519,7 +519,7 @@
 ; HYBRID-NEXT:    andq %r11, %rcx
 ; HYBRID-NEXT:    bsrq %rcx, %rdi
 ; HYBRID-NEXT:    xorq $63, %rdi
-; HYBRID-NEXT:    addq $64, %rdi
+; HYBRID-NEXT:    orq $64, %rdi
 ; HYBRID-NEXT:    testq %r8, %r8
 ; HYBRID-NEXT:    cmovneq %rbx, %rdi
 ; HYBRID-NEXT:    notq %rdx
@@ -565,7 +565,7 @@
 ; BURR-NEXT:    andq %r11, %rcx
 ; BURR-NEXT:    bsrq %rcx, %rdi
 ; BURR-NEXT:    xorq $63, %rdi
-; BURR-NEXT:    addq $64, %rdi
+; BURR-NEXT:    orq $64, %rdi
 ; BURR-NEXT:    testq %r8, %r8
 ; BURR-NEXT:    cmovneq %rbx, %rdi
 ; BURR-NEXT:    notq %rdx
@@ -614,7 +614,7 @@
 ; SRC-NEXT:    xorq $63, %r9
 ; SRC-NEXT:    bsrq %rcx, %rdi
 ; SRC-NEXT:    xorq $63, %rdi
-; SRC-NEXT:    addq $64, %rdi
+; SRC-NEXT:    orq $64, %rdi
 ; SRC-NEXT:    testq %r8, %r8
 ; SRC-NEXT:    cmovneq %r9, %rdi
 ; SRC-NEXT:    bsrq %rdx, %r9
@@ -663,7 +663,7 @@
 ; LIN-NEXT:    andq %rdx, %rcx
 ; LIN-NEXT:    bsrq %rcx, %rdx
 ; LIN-NEXT:    xorq $63, %rdx
-; LIN-NEXT:    addq $64, %rdx
+; LIN-NEXT:    orq $64, %rdx
 ; LIN-NEXT:    sbbq %r8, %r9
 ; LIN-NEXT:    notq %r8
 ; LIN-NEXT:    andq %r9, %r8
@@ -796,16 +796,16 @@
 ; ILP-NEXT:    xorq $63, %rcx
 ; ILP-NEXT:    bsrq %r10, %rsi
 ; ILP-NEXT:    xorq $63, %rsi
-; ILP-NEXT:    addq $64, %rsi
+; ILP-NEXT:    orq $64, %rsi
 ; ILP-NEXT:    testq %rdi, %rdi
 ; ILP-NEXT:    cmovneq %rcx, %rsi
 ; ILP-NEXT:    xorq $63, %rdx
 ; ILP-NEXT:    bsrq %rbx, %rcx
 ; ILP-NEXT:    xorq $63, %rcx
-; ILP-NEXT:    addq $64, %rcx
+; ILP-NEXT:    orq $64, %rcx
 ; ILP-NEXT:    testq %r11, %r11
 ; ILP-NEXT:    cmovneq %rdx, %rcx
-; ILP-NEXT:    subq $-128, %rcx
+; ILP-NEXT:    orq $128, %rcx
 ; ILP-NEXT:    xorl %r9d, %r9d
 ; ILP-NEXT:    orq %rdi, %r10
 ; ILP-NEXT:    cmovneq %rsi, %rcx
@@ -842,17 +842,17 @@
 ; HYBRID-NEXT:    xorq $63, %rcx
 ; HYBRID-NEXT:    bsrq %r10, %rdx
 ; HYBRID-NEXT:    xorq $63, %rdx
-; HYBRID-NEXT:    addq $64, %rdx
+; HYBRID-NEXT:    orq $64, %rdx
 ; HYBRID-NEXT:    testq %rdi, %rdi
 ; HYBRID-NEXT:    cmovneq %rcx, %rdx
 ; HYBRID-NEXT:    bsrq %r11, %rsi
 ; HYBRID-NEXT:    xorq $63, %rsi
 ; HYBRID-NEXT:    bsrq %rbx, %rcx
 ; HYBRID-NEXT:    xorq $63, %rcx
-; HYBRID-NEXT:    addq $64, %rcx
+; HYBRID-NEXT:    orq $64, %rcx
 ; HYBRID-NEXT:    testq %r11, %r11
 ; HYBRID-NEXT:    cmovneq %rsi, %rcx
-; HYBRID-NEXT:    subq $-128, %rcx
+; HYBRID-NEXT:    orq $128, %rcx
 ; HYBRID-NEXT:    orq %rdi, %r10
 ; HYBRID-NEXT:    cmovneq %rdx, %rcx
 ; HYBRID-NEXT:    xorl %r9d, %r9d
@@ -889,17 +889,17 @@
 ; BURR-NEXT:    xorq $63, %rcx
 ; BURR-NEXT:    bsrq %r10, %rdx
 ; BURR-NEXT:    xorq $63, %rdx
-; BURR-NEXT:    addq $64, %rdx
+; BURR-NEXT:    orq $64, %rdx
 ; BURR-NEXT:    testq %rdi, %rdi
 ; BURR-NEXT:    cmovneq %rcx, %rdx
 ; BURR-NEXT:    bsrq %r11, %rsi
 ; BURR-NEXT:    xorq $63, %rsi
 ; BURR-NEXT:    bsrq %rbx, %rcx
 ; BURR-NEXT:    xorq $63, %rcx
-; BURR-NEXT:    addq $64, %rcx
+; BURR-NEXT:    orq $64, %rcx
 ; BURR-NEXT:    testq %r11, %r11
 ; BURR-NEXT:    cmovneq %rsi, %rcx
-; BURR-NEXT:    subq $-128, %rcx
+; BURR-NEXT:    orq $128, %rcx
 ; BURR-NEXT:    orq %rdi, %r10
 ; BURR-NEXT:    cmovneq %rdx, %rcx
 ; BURR-NEXT:    xorl %r9d, %r9d
@@ -936,17 +936,17 @@
 ; SRC-NEXT:    xorq $63, %rcx
 ; SRC-NEXT:    bsrq %r10, %rdx
 ; SRC-NEXT:    xorq $63, %rdx
-; SRC-NEXT:    addq $64, %rdx
+; SRC-NEXT:    orq $64, %rdx
 ; SRC-NEXT:    testq %rdi, %rdi
 ; SRC-NEXT:    cmovneq %rcx, %rdx
 ; SRC-NEXT:    bsrq %r11, %rsi
 ; SRC-NEXT:    xorq $63, %rsi
 ; SRC-NEXT:    bsrq %rbx, %rcx
 ; SRC-NEXT:    xorq $63, %rcx
-; SRC-NEXT:    addq $64, %rcx
+; SRC-NEXT:    orq $64, %rcx
 ; SRC-NEXT:    testq %r11, %r11
 ; SRC-NEXT:    cmovneq %rsi, %rcx
-; SRC-NEXT:    subq $-128, %rcx
+; SRC-NEXT:    orq $128, %rcx
 ; SRC-NEXT:    orq %rdi, %r10
 ; SRC-NEXT:    cmovneq %rdx, %rcx
 ; SRC-NEXT:    xorl %r9d, %r9d
@@ -981,15 +981,15 @@
 ; LIN-NEXT:  # %bb.2: # %cond.false
 ; LIN-NEXT:    bsrq %rbx, %rcx
 ; LIN-NEXT:    xorq $63, %rcx
-; LIN-NEXT:    addq $64, %rcx
+; LIN-NEXT:    orq $64, %rcx
 ; LIN-NEXT:    bsrq %rdi, %rdx
 ; LIN-NEXT:    xorq $63, %rdx
 ; LIN-NEXT:    testq %rdi, %rdi
 ; LIN-NEXT:    cmoveq %rcx, %rdx
-; LIN-NEXT:    subq $-128, %rdx
+; LIN-NEXT:    orq $128, %rdx
 ; LIN-NEXT:    bsrq %r10, %rsi
 ; LIN-NEXT:    xorq $63, %rsi
-; LIN-NEXT:    addq $64, %rsi
+; LIN-NEXT:    orq $64, %rsi
 ; LIN-NEXT:    bsrq %r11, %rcx
 ; LIN-NEXT:    xorq $63, %rcx
 ; LIN-NEXT:    testq %r11, %r11